How to Lay a Patio — Step-by-Step UK Guide

What You'll Need

Before You Start

• Check for underground services — use a CAT scanner or contact your utility providers. This is especially important near the house where gas, water, electric and drainage pipes run.
• Ensure the finished patio level is at least 150mm below the damp-proof course (DPC) of your house. Building up against the DPC causes damp problems.
• Plan your drainage fall — the patio must slope away from the house at a minimum of 1:60.
• Order materials in advance. Use our Paving Slab Calculator to work out slab quantities and our Type 1 Sub-Base Calculator for aggregate volumes.
• Check the weather forecast — avoid laying slabs in rain, frost or extreme heat.

Step-by-Step Instructions

Step 1: Mark Out and Excavate

Mark out your patio area using string lines and pegs. Add 100mm to each side for edge haunching. Excavate to a depth of 200-250mm below your desired finished level (100mm sub-base + 30-40mm mortar bed + slab thickness). Keep the spoil — you may need it for backfilling edges.

Step 2: Compact the Sub-Grade

Once excavated, compact the exposed earth using a whacker plate. This prevents future settlement. If the ground is soft clay, lay a geotextile membrane before adding sub-base.

Step 3: Lay the Sub-Base

Spread Type 1 MOT crushed stone to a depth of approximately 125mm (it compacts to about 100mm). Compact in layers using the whacker plate — do not try to compact more than 75mm at once. Check levels regularly with a spirit level.

Step 4: Set Up Guide Lines

Set up string lines at the finished slab height. Establish your drainage fall (1:60 minimum away from the house). Use datum pegs at each corner and check with a spirit level.

Step 5: Mix the Mortar Bed

Mix a semi-dry mortar at a ratio of 4:1 (4 parts sharp sand to 1 part cement). The consistency should hold its shape when squeezed — not too wet. Spread a full mortar bed about 40mm thick for each slab. Do not use the five-dot method — a full bed gives much better support and prevents rocking.

Step 6: Lay the Slabs

Start from one corner, working away from the house. Place each slab onto the mortar bed and tap down with a rubber mallet until level with your string line. Leave 8-12mm gaps between slabs for jointing. Check each slab is level in both directions and maintains the drainage fall. Use spacers for consistent joint widths.

Step 7: Cut Edge Slabs

Mark cuts with a pencil and straight edge. Use an angle grinder with a diamond blade for clean cuts. Always wear safety goggles, ear defenders and a dust mask when cutting. Score the line first, then cut through in passes.

Step 8: Haunch the Edges

Mix a stronger mortar (3:1) and haunch the outside edges of the patio. The haunch should be triangular in profile, rising from the sub-base to about two-thirds up the edge of the slab. This prevents lateral movement.

Step 9: Joint the Slabs

Wait at least 24 hours before jointing. Use a resin-based jointing compound (e.g. Geofix or Nexus ProJoint) for the best results — it resists weeds and ants. Alternatively, use a 3:1 sand-cement dry mix brushed into joints and misted with water. Clean any excess off the slab faces immediately.

Step 10: Clean and Cure

Brush off any mortar residue. Allow 48-72 hours before walking on the patio. Keep off heavy furniture for a week. If rain is forecast before the mortar has set, cover with tarpaulin.

Common Mistakes to Avoid

• Skipping the sub-base: Laying slabs directly on soil or sand leads to sinking and uneven surfaces within a year.
• Not compacting properly: Insufficient compaction causes differential settlement and cracked slabs.
• Forgetting the drainage fall: Water pooling against your house causes damp. Always slope away at 1:60.
• Using the five-dot method: Placing five blobs of mortar under each slab leaves voids that fill with water and freeze in winter, cracking slabs.
• Building above the DPC: The finished patio must be at least 150mm below the damp-proof course.
• Not checking levels as you go: Check every slab — it is much harder to correct once the mortar has gone off.

Cost Estimate (2026 UK Prices)

Use our Paving Slab Calculator, Type 1 Sub-Base Calculator and Mortar Calculator for exact quantities for your project.